This invention relates to the field of robotics and, more particularly, to robotic systems incorporating dynamic optical sensing and to manufacturing methods utilizing same.
Current research in robotics is to a large extent devoted to sensors which extend the capabilities of a robot in two ways. First, sensors are used by the robot to acquire a target object. Second, once the object has been acquired, the robot uses sensors to inspect and guide manipulation of the object. The first class of sensors (acquisition sensors) includes vision and proximity sensors. A magnetic proximity sensor is described by G. Beni et al. in copending application Ser. No. 480,826 filed on Mar. 31, 1983 and assigned to the assignee hereof. The second class (inspection-manipulation sensors) includes tactile and force-torque sensors of the type described by G. Beni et al. in copending application Ser. No. 498,908 filed on May 27, 1983, which is also commonly assigned. Generally, sensors of the acquisition type operate without contacting the object, whereas sensors of the inspection-manipulation type come in contact with the object.
For most sensors proposed and/or implemented in the prior art, the sensing field is constant in time as, for example, in a fixed camera or a tactile pad. Exceptions are cameras mounted on robot hands described by M. Shneier et al. at the Workshop on Industrial Applications of Machine Vision, Washington, D.C. (1982), and fingertip sensors for a three-fingered robot hand described by J. K. Salisbury, Proceedings of the Joint Automation Control Conference, University of Virginia, Charlottesville, Virginia, p. TA2C (1981). In both of these cases, robot-manipulation is used to increase the sensory information about the object investigated; i.e., the sensing is a dynamic process.
However, most of the current vision systems, as described by R. P. Kruger et al., Proceedings of the IEEE, Vol. 69, p. 1524 (1981), use static overhead cameras placed above the robot working area. This static arrangement has the advantage of decoupling the calculation of position and orientation of the object from the robot motion. The robot is not slowed down by the vision system, which operates independently. This static arrangement, however, has a major drawback. The vision system is ineffective when it is most needed; i.e., when the robot is about to retrieve a part, since the robot arm blocks the field of view of the camera placed above the robot working area. To overcome this problem, camera-in-hand systems have been proposed and implemented. This method has the advantage of never hiding from the camera the part to be acquired. However, the robot must stop its motion to allow the camera to process the image and calculate position and orientation of the part.
Recently this problem has been alleviated by using a low-resolution camera, see, C. Loughlin, Sensor Review, Vol. 3, p. 23 (1983), rigidly fixed to the robot gripper. An example is the Insight 32.TM. system (Insight 32 is a trademark of Unimation Corporation of Danbury, Conn.). This system uses a camera with a resolution of 32.times.32 pixels. At this low resolution, the scan time is 20 msec and the processing time for simple binary vision algorithms can be kept below 8 msec so that part location is effected within the allotted 28 msec of a typical robot loop cycle (e.g., a Puma 500.TM. robot; Puma 500 is also a trademark of Unimation Corporation). Clearly, this low-resolution mobile vision system is an improvement over the traditional high resolution static camera method because 70% of industrial applications do not require part recognition but only part location and orientation. On the other hand, even with a mobile camera the process of part location and orientation is still limited by the binary vision system, which basically sees only silhouettes of images. In addition, this vision system has exacting requirements for contrast (e.g., backlit tables, white surfaces, etc.). To improve the efficiency of orientation-location, this type of mobile vision system can be complemented by dynamic sensing in accordance with our invention.